Martin Danneberg

Experimental testbed for 5G cognitive radio access in 4G LTE cellular systems

Cognitive radio technology addresses the limited availability of wireless spectrum and inefficiency of spectrum usage. Cognitive Radio (CR) devices sense their environment, detect spatially unused spectrum and opportunistically access available spectrum without creating harmful interference to the incumbents. In cellular systems with licensed spectrum, the efficient utilization of the spectrum as well as the protection of primary users is equally important, which imposes opportunities and challenges for the application of CR. This paper introduces an experimental framework for 5G cognitive radio access in current 4G LTE cellular systems. It can be used to study CR concepts in different scenarios, such as 4G to 5G system migrations, machine-type communications, device-to-device communications, and load balancing. Using our framework, selected measurement results are presented that compare Long Term Evolution (LTE) Orthogonal Frequency Division Multiplex (OFDM) with a candidate 5G waveform called Generalized Frequency Division Multiplexing (GFDM) and quantify the benefits of GFDM in CR scenarios.

Field trial evaluation of UE specific antenna downtilt in an LTE downlink

The benefits of horizontal beamforming in cellular networks are well unterstood, and the technology is already used in commercial products. Recently, vertical beamforming (basically a user specific downtilt (DT)) receives a lot of attention as well. However, available channel models do not allow for an accurate simulation of this transmission scheme. This publication investigates the impact of antenna DT in a typical urban area using field trials. Two models are presented and compared with measurement data in order to study their value and limitations for the evaluation of vertical beamforming, which is an important basis for planning and deploying of such schemes in order to increase cellular downlink (DL) throughput.

Experimental Testbed for Dynamic Spectrum Access and Sensing of 5G GFDM Waveforms

Generalized frequency division multiplexing (GFDM) is a new candidate waveform for 5G applications. With flexible pulse shaping filtering and tail-biting cyclic prefix, GFDM has lower out of band leakage and hence is more suitable as an opportunistic cognitive radio waveform. Improved adjacent channel leakage ratio (ACLR) of GFDM makes the coexistence of secondary signals easier, with lower adjacent channel interference to legacy users. This paper details the experimental validation of the coexistence study of this 5G waveform in an LTE system. The paper also highlights the improved sensing performance of GFDM- CR waveform compared to traditional OFDM. OFDM with implicit rectangular pulse shaping has higher out of band leakage and increases the probability of false alarm; while sharper GFDM waveform demonstrates substantial spectral efficiency and produces lesser number of false alarms.

Experimental analysis and simulative validation of dynamic spectrum access for coexistence of 4G and future 5G systems

5G mobile networks will very likely include features that allow for a dynamic spectrum access (DSA) in order to exploit spectrum holes of a primary system. The efficient utilization of spectrum holes with minimum impairment of the primary system requires a waveform with a very low adjacent channel leakage ratio as well as robustness to time and frequency offsets. One of the approaches for new waveforms is Generalized Frequency Division Multiplexing (GFDM), a digital multi-carrier transceiver concept that employs pulse shaping filters to provide control over the transmitted signals spectral properties. In this paper we present experimental results that evaluate the impact of the new GFDM waveform on an existing 4G system. The 4G system was based on Eurecoms OpenAirInterface for the eNB and a commercial UE. The 5G system was emulated using the LabVIEW/PXI platform with corresponding RF adapter modules from National Instruments and TUDs GFDM implementation. The experimental results show that GFDM can be used with about 5 dB higher transmit power than a corresponding orthogonal frequency division multiplexing (OFDM) system, before any impact on the primary system is noticeable. The results from our real-time measurements were validated by simulations.

Implementation of a 2 by 2 MIMO-GFDM transceiver for robust 5G networks

The fifth generation (5G) of mobile cellular systems will demand an unprecedented flexibility of the physical layer (PHY). Several approaches are being proposed based on theoretical and simulation analyses, but there is a lack of implementations that allow for performance evaluation under real channel conditions and front-end impairments. In this paper we show that that a 2×2 multiple-input multiple-output (MIMO) Generalized Frequency Division Multiplexing (GFDM) transceiver can be implemented using the new National Instruments USRP-RIO, which proves that todays technology is ready to afford the complexity of modern waveforms. In this implementation we explore the flexibility of the USRP combined with LabVIEW, allowing for an easy integration between software host processing and real-time processing based on Field Programmable Gate Arrays (FPGAs). This implementation allows to evaluate different GFDM characteristics, such as reduced latency, low out-of-band (OOB) emission and increased robustness in real-world environment.

Flexible GFDM Implementation in FPGA with Support to Run-Time Reconfiguration

Innovative 5G applications will challenge future cellular systems with new requirements. The OFDM based 4G standard will not be able to address all of them. Generalized frequency division multiplexing is a flexible multicarrier waveform with additional degrees of freedom. This paper presents a strategy towards a flexible FPGA implementation of GFDM, which is reconfigurable at run-time.

Generalized Frequency Division Multiplexing: A Flexible Multi-Carrier Waveform for 5G

The next generation of wireless networks will face different challenges from new scenarios. The conventional Orthogonal Frequency Division Multiplexing (OFDM) has shown difficulty in fulfilling all demanding requirements. This chapter presents Generalized Frequency Division Multiplexing (GFDM) as a strong waveform candidate for future wireless communications systems which can be combined with several techniques such as precoding or Offset Quadrature Amplitude Modulation (OQAM) and which offers the flexibility to emulate a variety of other popular waveforms as corner cases. This property suggests GFDM as a key technology to allow reconfiguration of the physical layer (PHY), enabling a fast and dynamic evolution of the infrastructure. Additionally, multicarrier transmission theory is covered in terms of Gabor theory. Details on synchronization, channel estimation algorithms and MIMO techniques for GFDM are presented and a description of a proof-of-concept demonstrator shows the suitability of GFDM for future wireless networks.

Flexible Physical Layer Design

Introduction The role of software in mobile communication systems has increased over time. For the upcoming fifth generation (5G) mobile networks, the concept of software-defined networking (SDN) can ease network management by enabling anything as a service. Software-defined radio (SDR) enables radio virtualization, where several radio components are implemented in software. Cognitive radio (CR) goes one step further by using a software-based decision cycle to self-adapt the SDR parameters and consequently optimize the use of communication resources. This proposal leads to the possibility of having real-time communication functionalities at virtual machines in cloud computing data centers, instead of deploying specialized hardware. Network functions virtualization (NFV) claims to provide cloud-based virtualization of network functionalities. The perspective is that all these software-based concepts should converge while 5G networks are being designed. A new breakthrough will be achieved when all these software paradigms are applied to the physical layer (PHY), where its functionalities are defined and controlled by software as well. A flexible PHY design is particularly beneficial considering the diverse applications proposed for 5G [1]. In fact, these applications typically have conflicting design objectives and face extreme requirements. Broadband communication will play an important role in, for instance, offering video streaming services with high resolution for TV and supporting high-density multimedia such as 4K and 3D videos in smartphones. Data rates up to 10 gigabits per second (Gbps) are therefore being targeted in 5G. The Tactile Internet [2] enables one to control virtual or real objects via wireless links with haptic feedback. This implies that the end-to-end latency constraint in 5G must be dropped by at least one order of magnitude compared with current fourth generation (4G) technologies. The Internet of Things (IoT) is aimed at connecting a massive amount of devices. Wireless sensor networks need to provide in-service monitoring at low cost and with a long battery life. Smart vehicles improve safety and actively avoid accidents by exchanging their driving status, such as position, breaking, acceleration, and speed, with surrounding vehicles and infrastructure via challenging doubly dispersive channels. Overall, this demands asynchronous multiple access, ultra-low latency, and ultra-high reliability.

Ray-tracing wireless channel modeling and verification in Coordinated Multi-Point systems

Coordinated Multi-Point (CoMP) Multiple Input Multiple Output (MIMO) transmission improves users coverage and data throughput particularly on the cell edges. To make full advantage of CoMP, radio planning tools need very accurate models that fully capture the MIMO channels characteristics. This paper presents detailed modeling and analysis of an uplink CoMP system using Ray-Tracing (RT)-based channel modeling. The contribution of this paper is to show how close RT simulations can predict end-to-end system performance compared to the real-world measured performance. Thorough drive test measurements and RT simulations were performed. CoMP and Conventional MIMO systems performances are evaluated and compared for measured and RT-simulated channels. The results of several scenarios show that the RT matches the measurements in terms of rates and geometrical properties. The CoMP gain resulting from the measurements is almost double the gain of RT simulations. The differences come from the hardware and the RT 3D models impairments.